Method and system for copper interconnect formation

ABSTRACT

A system and method for reducing contamination in a semiconductor device formed on a substrate is disclosed. The method and system include providing a barrier metal layer on the substrate. A first portion of the barrier metal layer is thinner than a second portion of the barrier metal layer. The method and system further include removing the first portion of the barrier metal layer.

FIELD OF THE INVENTION

[0001] The present invention relates to semiconductor processing andmore particularly to a method and system for reducing the contaminationdue to copper interconnect formation.

BACKGROUND OF THE INVENTION

[0002] Copper interconnects can be used formed during semiconductorprocessing. In forming copper interconnects, for a trench is firstprovided in the silicon substrate. Next, a barrier metal is typicallydeposited to prevent the copper to be used in an interconnect or viafrom migrating. Then, copper plating is performed, filling the trenchand providing the interconnect.

[0003] Typically, the barrier metals that are used also work as a seedlayer for copper. Such barrier metals are used to allow the growth ofthe copper on the barrier metal in the trench or the via. If barriermetals which cannot act as a seed layer are used, the copper will notproperly grow in the trench or via unless a separate seed layer isprovided.

[0004] Although the above process forms copper interconnects, thebarrier metal is deposited at the edge and rear of the silicon substrateas well as in the trenches or vias. Because the barrier metal acts as aseed layer for copper, a copper film also develops at the edge and rearof the substrate during copper plating. Because this copper film isthin, it does not adhere well to the silicon substrate and peels duringprocessing. Pieces of the peeled copper film may then contaminate thecircuitry formed towards the center of the silicon substrate.

[0005] Accordingly, what is needed is a system and method for providingcopper interconnects and vias without introducing copper contaminationdue to films formed at the edge of the substrate. The present inventionaddresses such a need.

SUMMARY OF THE INVENTION

[0006] The present invention provides a method and system for reducingcontamination in a semiconductor device formed on a substrate. A firstportion of the barrier metal layer is thinner than a second portion ofthe barrier metal layer. The method and system further comprise removingthe first portion of the barrier metal layer.

[0007] According to the system and method disclosed herein, the presentinvention reduce copper contamination, thereby increasing overall systemperformance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a block diagram of a conventional system for providingcopper interconnects.

[0009]FIG. 2A is a block diagram of a system for providing copperinterconnects in accordance with the method and system just afterdeposition of a barrier metal layer.

[0010]FIG. 2B is a block diagram of a system for providing copperinterconnects in accordance with the method and system during etching.

[0011]FIG. 2C is a block diagram of a system for providing copperinterconnects in accordance with the method and system after etching.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention relates to an improvement in semiconductorprocessing. The following description is presented to enable one ofordinary skill in the art to make and use the invention and is providedin the context of a patent application and its requirements. Variousmodifications to the preferred embodiment will be readily apparent tothose skilled in the art and the generic principles herein may beapplied to other embodiments. Thus, the present invention is notintended to be limited to the embodiment shown but is to be accorded thewidest scope consistent with the principles and features describedherein.

[0013]FIG. 1 is a block diagram of a conventional substrate duringformation of copper interconnects and vias. The substrate 12 istypically silicon. The substrate is placed on an apparatus including abase 18. After formation of trenches or via holes, not shown, a layer ofbarrier metal 14 is deposited onto the substrate 14. The barrier metallayer 14 is used to block the migration of copper outside of theinterconnects and vias. Typically, the barrier metal layer 14 is formedthrough chemical vapor deposition (“CVD”). In some instances a seedlayer 16 is also grown on the barrier metal layer 14. After the seedlayer 16 is provided, a copper layer, not shown, is deposited.Typically, the copper layer is formed by electroplating copper.

[0014] Although the system shown in FIG. 1 allows formation of copperinterconnects and vias, those with ordinary skill in the art willrealize that copper deposited during formation of the interconnects andvias will contaminate the structures formed on the substrate 12. Thebarrier metal layer 14 covers not only the open portion, but also coversthe edge and a portion of the back of the substrate 12. Thus, a thinlayer of the barrier metal chosen for the barrier metal layer 14 ispresent at the edge and rear of the substrate 12. Typically, the barriermetal layer 14 is approximately 300 Angstroms near the center of thesubstrate 12 and approximately 30 Angstroms at the edge and rear of thesubstrate 12.

[0015] The barrier metal layer 14 can typically act as a seed layer forcopper. For example, tungsten-nitride (WN_(x) where x is an integer) ortitanium-nitride (TiN) is typically used to form the barrier metal layer14. This feature of the barrier metal layer 14 is important in aidingthe growth of the copper to form the interconnects and vias. Because thebarrier metal layer 14 is a seed layer, the copper plating causes a thinlayer of copper, not shown, to grow on the thin portion of the barriermetal layer 14, at the edge and back of the substrate 12. The thincopper layer does not adhere well to the substrate 12. As a result, thethin copper layer peels off of the edge and back of the substrate 12,contaminating the circuits formed on the substrate 12.

[0016] The present invention provides for a method and system forremoving a portion of the barrier metal layer. The present inventionwill be described in terms of a particular process for etching a portionof the barrier metal layer. However, one of ordinary skill in the artwill readily recognize that this method and system will operateeffectively for other types of methods for removing the portion of thebarrier metal layer.

[0017] To more particularly illustrate the method and system inaccordance with the present invention, refer now to FIG. 2A depicting ablock diagram of one embodiment of such a system 100 just afterdeposition of a barrier metal. The system 100 of the present inventionincludes a base 118. The substrate 112 is placed on the base 118.Trenches or vias are then formed in the substrate 112. Next, a barriermetal layer 114 is deposited to prevent diffusion of any copperdeposited later. In a preferred embodiment, the barrier metal layer 114is deposited using CVD. Typically, the barrier metal layer 114 is muchthicker near the center of the substrate 112 than near the edge. In apreferred embodiment, the barrier metal layer 114 is approximately threehundred Angstroms near the center at approximately thirty Angstroms nearthe edge of the substrate 114. Generally, the barrier metal layer 114 ison the order of ten times thicker at the center of the substrate 112than at the edge and back of the substrate 112. After deposition of thebarrier metal layer 114, a seed layer 116 is deposited. The seed layer116 improves adhesion of the copper layer, not shown, which is to bedeposited later. FIG. 2B depicts the system 100 after deposition of theseed layer 116.

[0018] In accordance with the method and system, the barrier metal layer114 is etched after deposition of the seed layer 116. This etch removesthe thin portions of the barrier metal layer 114 at the edge and back ofthe substrate. In a preferred embodiment, if the barrier metal layer 114is composed of tungsten nitride, the etching gas is preferably NF₃. Inanother embodiment, if the barrier metal layer 114 is composed oftitanium nitride, the etching gas used may be chlorine.

[0019] Etching the barrier metal layer 114 removes the portion of thebarrier metal layer 114 at the edge and back of the substrate 112.Because of the presence of the seed layer 116, the metal in the centralportion of the substrate 112 is not significantly etched. This removesthe thinner portion of the barrier metal layer 114. Typically, thethinner portion of the barrier metal layer 114 is at the edge and backof the substrate 112. Thus, the etch removes the portion of the barriermetal layer 114 to which copper would otherwise adhere. Because of theseed layer 116, the thinner portions of the barrier metal layer 114 havebeen removed while the thicker portion of the barrier metal layer 114lying beneath the seed layer 116 remains substantially unchanged. Thus,in accordance with the method and system, the thin portion of thebarrier metal layer 114 will be removed.

[0020] Refer now to FIG. 2C, depicting one embodiment of the system 100after etching of the barrier metal layer 114. The thin portions of thebarrier metal layer 114 have been removed, leaving only the thickercentral portion lying beneath the seed layer 116. Because the portion ofthe barrier metal layer at the edge and back of the substrate 114 wasetched while the portion of the barrier metal layer at the center of thesubstrate 114 was protected by the seed layer 116, the portion of thebarrier metal layer 114 remaining can still prevent diffusion of thecopper, not shown, that will be plated later. In addition, because theportion of the barrier metal layer 114 at the edge and back of thesubstrate 112 has been removed, there is no seed layer for copper toadhere to at these portions of the substrate. As a result, deposition ofcopper at the edges and back of the substrate is greatly reduced. Thecontamination due to copper peeling off of the substrate 112 is therebyreduced.

[0021] A method and system has been disclosed for providing copperinterconnects with reduced contamination due to copper deposited at theedge or rear of the substrate.

[0022] Although the present invention has been described in accordancewith the embodiments shown, one of ordinary skill in the art willreadily recognize that there could be variations to the embodiments andthose variations would be within the spirit and scope of the presentinvention. Accordingly, many modifications may be made by one ofordinary skill in the art without departing from the spirit and scope ofthe appended claims.

What is claimed is:
 1. A method for reducing contamination in asemiconductor device formed on a substrate comprising the steps of:providing a barrier metal layer on the substrate, a first portion of thebarrier metal layer being thinner than a second portion of the barriermetal layer; and removing the first portion of the barrier metal layer.2. The method of claim 1 wherein the substrate further includes acenter, an edge, a front, and a back; the first portion of the barriermetal layer being near the substrate edge and back, the second portionof the barrier metal layer being near the substrate center.
 3. Themethod of claim 2 further comprising the steps of: providing a seedlayer located near the center of the substrate.
 4. The method of claim 3wherein the step of removing the portion of the barrier metal layer nearthe substrate edge and substrate back further comprises the step of:etching the first portion of the barrier metal layer using an etchinggas.
 5. The method of claim 4 wherein the barrier metal layer furthercomprises tungsten nitride; and the etching gas further comprises NF₃.6. The method of claim 4 wherein the barrier metal layer furthercomprises titanium nitride; and the etching gas further compriseschlorine.
 7. A system for reducing contamination in a semiconductordevice formed on a substrate comprising: means for providing a barriermetal layer on the substrate, a first portion of the barrier metal layerbeing thinner than a second portion of the barrier metal layer; andmeans for removing the first portion of the barrier metal layer.
 8. Thesystem of claim 7 wherein the substrate further includes a center, anedge, and a back; and the first portion of the barrier metal layer beingnear the substrate edge and back, the second portion of the barriermetal layer being near the substrate center.
 9. The system of claim 8further comprising: means for providing a seed layer located near thesubstrate center.
 10. The system of claim 9 further comprising: a basefor supporting the substrate at the back of the substrate.
 11. Thesystem of claim 10 wherein the means for removing the first portion ofthe barrier further comprise: means for etching the barrier metal layerusing an etching gas.
 12. The system of claim 11 wherein the barriermetal layer further comprises tungsten nitride; and the etching gasfurther comprises NF₃.
 13. The system of claim 11 wherein the barriermetal layer further comprises titanium nitride; and the etching gasfurther comprises chlorine.